Polarizer-equipped optical fiber ferrule, connector and connector adaptor

ABSTRACT

The present invention provides a polarizer-attached optical fiber ferrule, a polarizer-attached optical fiber connector, and a polarized-attached optical fiber connector adapter for coupling a linear polarizer with one or more optical fibers without employing a lens. The polarizer-attached optical fiber connector  2  is equipped with an optical fiber  10 , a ferrule  5  fitted on the periphery of the optical fiber  10  and equipped with a slit  16  reaching the optical fiber  10 , and a linear polarizer  18  inserted into the slit  16  so that it crosses the optical fiber  10.

TECHNICAL FIELD

The present invention relates to a polarizer-attached optical fiberferrule, a polarizer-attached optical fiber connector, and apolarized-attached optical fiber connector adapter.

BACKGROUND ART

It is known that optical fiber technology has a wide variety ofapplications in communication systems. Copper lines, coaxial cables, andin certain cases microwave relays and satellites, have been replacedwith optical fiber communication systems. Optical fiber systems areparticularly attractive with regard to long-distance communication,because it has the ability to transmit enormous information and is lesssusceptible to electromagnetic interference. Optical fiber links areuseful in transmitting a signal over an extremely short distance, forexample, between a large general-purpose computer and its peripheralequipment. Optical fiber transmission systems are also employed totransmit a signal between circuit boards within a computer. Variousinvestigations have also been made with respect to the connection ofoptical fibers at a low level, such as the connection betweenmicrochips. Optical fiber systems are also employed as sensors forsensing pressure, liquid level, temperature, magnetic field, acidity,and other stimuli. These optical fiber sensors are generally based on aconversion mechanism that depends on a change in the polarization oflight passing through the sensors. The light polarization is changed byan external stimulus.

Optical fiber systems are equipped with three main components, whichinclude a transmitter for converting a data signal to an optical signal,an optical fiber for guiding the optical signal, and a receiver forcapturing the optical signal at the other end of the optical fiber andconverting it to an electrical signal. A light source in the transmittercan be a semiconductor laser diode or a light-emitting diode (LED). AnLED is a light source of relatively low output which operates at a lowerdata transmission ratio than that of a laser diode. For applicationsrequiring high-speed data transmission or long-distance communication, alaser diode is preferred. Light emitted from a light source is modulatedto convert an optical signal to a data signal.

The linearly polarized light produced by the semiconductor laser diodeis very effective in many communication or measurement systems employingoptical fibers. However, the extinction ratio of light emitted from thelaser diode is approximately 20 dB, and this value is not always stable.Also, it cannot be said that the extinction ratio is sufficiently highfor many applications. For instance, there is demand for an extinctionratio of 40 dB or greater. To meet this demand for a laser light havingsuch a high extinction ratio, a laser module with a polarized-waverotating function has been put into practical use as a light source, andin an optical transmission path, a fiber polarizer, etc., have been putinto practical use. These elements generally require the followingtechnique and construction. The technique and construction is to passlaser light through a linear polarizer having a higher extinction ratiothan that of the laser light being guided. To achieve the technique andconstruction, a multiplicity of methods have been proposed.

A linear polarizer that is employed for the aforementioned object isused as a single element. A Glan-Thompson prism, a PBS, POLARCOR (tradename), etc., are polarizers that are commonly used. These linearpolarizers generally require a lens system to couple with an opticalfiber. A lens that is employed in the lens system is generally costly,and it is necessary to align the lens with an optical fiber in threedimensions with submicron accuracy to couple them. This alignment stepis extremely complicated and difficult. Therefore, there is demand for areduction in the number of components and simplification of thealignment step.

If the thickness of a polarizer is so thin that there is no considerableloss, when disposed between optical waveguides, a lens will not berequired in order to couple the polarizer with the optical fiber.Furthermore, a certain construction makes it possible to apply apolarizer without a complicated alignment step. As a linear polarizerwith such an extremely thin thickness, there is known “LAMIPOL” (tradename) whose thickness is about 30 μm. “LAMIPOL” is employed inoptical-fiber applications employing no lens. However, the effectiveaperture of“LAMIPOL” is so small that the resultant assembly step isfairly difficult. Therefore, the step is still complicated. Since“LAMIPOL” has a laminated structure, the optical characteristics varylargely because of a change in the incidence angle of light. Because ofthis, the inclination of an element for suppression of reflected returnlight cannot be utilized. This element inclination is indispensable foroptical-fiber applications and puts restrictions on the application of“LAMIPOL.” In addition, since “LAMIPOL” consists of alternate layers ofwhich thermal expansion coefficients are significantly different, thereis another problem that the optical characteristic will be lost byhigh-energy irradiation such as high-power laser irradiation andhigh-temperature processing. Therefore, “LAMIPOL” is limited toapplications where light intensity is relative low, as in fiberpolarizers and polarized-light output fiber collimators. Thus, anoptical system employing “LAMIPOL” has the advantage of not using alens, but, as described above, is rather restricted in applicable use.

On the other hand, a wavelength selecting filter, which is employed forwavelength-multiplexing communication employing optical fibers, can bemade nearly the same thickness as the above-mentioned “LAMIPOL.”Therefore, the wavelength selecting filter can be applied to opticalfibers without using lenses. For example, a slit is formed in aconnector so that it crosses an optical fiber, and the wavelengthselecting fiber is inserted into the slit. In addition, some wave platesmade of polyimide, etc., can be formed to a thickness less than theaforementioned thickness, and there has also been provided an elementwith a slit into which a wave plate is inserted. These filters requireno lens because they are thin. However, since the optical characteristicof the optical filter depends largely on an angle of incidence, anadditional design is required for the filter, and the slit needs to beformed with a high degree of accuracy so that the filter can be insertedat a desired angle.

SUMMARY OF THE INVENTION

The present invention has been directed to an optical fiber connectorand an optical fiber connector adapter that are inevitably employed asconnectors in both a light source and an optical transmission path.Furthermore, the invention has been directed to an optical fiber ferrulethat is always used in both the optical fiber connector and the opticalfiber connector adapter. It is an object of the present invention toprovide a polarizer-attached optical fiber ferrule, a polarizer-attachedoptical fiber connector, and a polarizer-attached optical fiberconnector adapter that are capable of producing laser light which has ahigh extinction ratio.

Another object of the present invention is to provide apolarizer-attached optical fiber ferrule, a polarizer-attached opticalfiber connector, and a polarizer-attached optical fiber connectoradapter which are capable of reducing the number of components and themanufacturing costs, as well as facilitating the manufacturing step.

In accordance with the present invention, there is provided apolarizer-attached optical fiber ferrule comprising: an optical fiber; aferrule, fitted on the periphery of the optical fiber, and equipped witha slit reaching the optical fiber; and a linear polarizer inserted intothe slit so that it crosses the optical fiber.

Also, there is provided a polarizer-attached optical fiber connectorcomprising: an optical fiber; a connector ferrule, fitted on theperiphery of the optical fiber, and equipped with a slit reaching theoptical fiber; and a linear polarizer inserted into the slit so that itcrosses the optical fiber.

In addition, there is provided a polarizer-attached optical fiberconnector adapter comprising: an optical fiber; two adapter ferrules,fitted on the periphery of the optical fiber, and fixed within analignment sleeve; and a linear polarizer inserted between the ferrules.

Furthermore, there is provided a polarizer-attached optical fiberconnector adapter comprising: an optical fiber; an adapter ferrule,fitted on the periphery of the optical fiber, and equipped with within aslit reaching the optical fiber; and a linear polarizer inserted intothe slit so that it crosses the optical fiber.

The above-mentioned linear polarizer may be a dichroic glass polarizer.The aforementioned slit may be inclined with respect to an axialdirection of the optical fiber.

The aforementioned fiber may be a single-mode fiber or, and morepreferably polarized-wave holding fiber.

It is preferable that the aforementioned linear polarizer have apolarizing angle which aligns with a polarization direction of a laserbeam. The aforementioned optical fiber may comprise one or more opticalfibers.

The polarizer-attached optical fiber ferrule, the polarizer-attachedoptical fiber connector, and the polarizer-attached optical fiberconnector adapter of the present invention are equipped with a ferrulewith a slit reaching an optical fiber, and a linear polarizer insertedinto the slit so that it crosses an optical fiber. Therefore, they donot require an additional component such as a lens, etc. Also, sinceonly the linear polarizer is inserted into the slit, a complicatedalignment step is unnecessary. These render it possible to produce laserlight that has a high extinction ratio. In addition, the number ofcomponents and the manufacturing costs can be reduced and themanufacturing step can be facilitated.

Furthermore, the polarizer-attached optical fiber connector adapter ofthe present invention is equipped with the two ferrules fixed within analignment sleeve, and the linear polarizer inserted between theferrules. Therefore, laser light with a high extinction ratio can beproduced. In addition, the number of components and the manufacturingcosts can be reduced and the manufacturing step can be facilitated.

In the case where the above-mentioned linear polarizer is a dichroicglass polarizer, it can absorb all the unpolarized components. Inaddition, in the case where the aforementioned slit is inclined withrespect to the axial direction of the optical fiber, reflected returnlight becomes so small that it is negligible.

In the case where the aforementioned fiber is a single-mode fiber, it issuitable for high-volume transfer requiring broad-band characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a polarizer-attached optical fiberferrule according to a first embodiment of the present invention;

FIG. 2 is a sectional view showing a polarizer-attached optical fiberconnector according to a second embodiment of the present invention;

FIG. 3 is a diagram showing a polarizer-attached optical multi-fiberconnector according to a third embodiment of the present invention;

FIG. 4 is a sectional view showing a polarizer-attached optical fiberconnector adapter according to a fourth embodiment of the presentinvention; and

FIG. 5 is a sectional view showing a polarizer-attached optical fiberconnector adapter according to a fifth embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings.According to the embodiments of the present invention, there areprovided a polarizer-attached optical fiber ferrule, apolarizer-attached optical fiber connector, and a polarizer-attachedoptical fiber connector adapter which couple a linear polarizer with oneor more optical fibers without employing a lens system. The basicprinciple of the embodiments of the present invention is that the linearpolarizer is inserted into the ferrule so that it crosses the opticalfiber. The linear polarizer is inserted into a slit formed in theferrule so that it crosses the optical fiber.

The effectiveness of the polarizer-attached optical fiber ferrule, thepolarizer-attached optical fiber connector, and the polarizer-attachedoptical fiber connector adapter depends on the selection of the linearpolarizer. It is preferable that the linear polarizer be very thin inorder to minimize the coupling loss. It is preferable that the thicknessof the linear polarizer be about 50 μm or less. The linear polarizershould have an extinction ratio far higher than that of a laser diode toenhance the extinction ratio of the laser diode. Furthermore, it isnecessary that the linear polarizer be a dichroic polarizer whichabsorbs one polarization component and transmits the other polarizationcomponent. It is preferable that the linear polarizer have highresistance to laser-irradiation damage. It is preferable that the linearpolarizer have a large aperture so that it is easily fitted on anoptical fiber so as to cross the optical fiber. It is preferable thatthe linear polarizer be practically insensitive to a change in an angleof incidence, that is, have a large acceptance angle, so that in orderto reduce reflected light that returns to the incident side, thepolarizer can be disposed at an angle inclined slightly from a planevertical to the optical axis of the fiber. It is preferable that thelinear polarizer have the same refractive index as that of an opticalfiber core, that is, an optical waveguide.

Now, various embodiments of the present invention will be described withreference to the drawings. FIG. 1 shows a schematic diagram of apolarizer-attached optical fiber ferrule 42 equipped with a slit 43reaching an optical fiber. The ferrule 42 has a center pore 45 to whicha bare fiber 41 is inserted and fixed. The slit 43 is formed in theferrule 42 so that it crosses the bare fiber 41. A linear polarizer 44is inserted into the slit 43, which is in turn formed at an angleinclined slightly from a plane vertical to the axis direction of thebare fiber 41. This polarizer-attached optical fiber ferrule 42 is thebasis of the present invention. The present invention includes any typeof optical component, for example, an optical fiber connector, anoptical fiber connector adapter, etc., as long as it employs the ferrule42. FIG. 1 shows the single-fiber ferrule to which a single fiber isfixed. However, the present invention is also applicable to amulti-fiber ferrule to which two or more fibers are fixed. Subsequently,a description will be given of applications equipped with thepolarizer-attached optical fiber ferrule 42.

FIG. 2 shows a polarizer-attached optical fiber connector 2 equippedwith a connector ferrule 4. The connector ferrule 4 includes a ferrule 5formable with ceramic material, and has a center pore 6 into which thebare fiber portion 8 of an optical fiber 10 is inserted. The ferrule 5is fixed by a ferrule supporting body 12 such as a metal fixing flange.The ferrule supporting body 12 is equipped with a center pore 14 forreceiving part of the bare fiber portion 8 of the optical fiber 10. Aslit 16 is formed from the ferrule supporting body 12 toward the barefiber portion 8. This slit 16 is formed at an angle inclined slightlyfrom a plane vertical to the bare fiber portion 8. When the ferrule 5has sufficient mechanical strength, the slit 16 may be formed in theferrule 5 near the ferrule supporting body 12.

Referring to FIG. 2, a linear polarizer 18 is inserted into the slit 16.This linear polarizer 18 can be fixed, for example, with an adhesive.The linear polarizer 18 may be provided with a rotation mechanism (notshown) to obtain a desired polarization direction as required, byrotating the plane of the linear polarizer 18 vertical to the opticalaxis direction of the optical fiber 10.

The polarizer-attached optical fiber connector 2 is employed in a lasermodule (not shown), and the rotation axis of the polarizer 18 can bealigned with the polarization axis of laser light produced by a laserdiode. With this alignment, if only the polarizer-attached optical fiberconnector 2 is connected to a laser module whose extinction ratio islow, it becomes possible to produce laser light that has a highextinction ratio. In addition, since the polarizer 18 is of a dichroictype, as described above, all of the unpolarized components areabsorbed. Furthermore, the polarizer 18 is fixed at an angle inclinedslightly from a plane vertical to the optical axis of the optical fiber10 so that the return light reflected by the polarizer 18 is negligible.Therefore, the laser oscillation can be stably held. That is, it becomespossible to enhance the characteristics of ordinary laser modules.

The polarizer-attached optical fiber connector 2 can also be applied tocommon connectors that are employed in optical transmission path. Inthis case, the extinction ratio of light propagating through an opticaltransmission path can be enhanced. That is, the polarizer-attachedoptical fiber connector fulfills the same function as the fiberpolarizer.

The above-mentioned polarizer-attached optical fiber connector 2requires no addition of an optical component (a lens, etc.) and nospecial design, because it is manufactured by forming thelinear-polarizer inserting slit 16 in a commonly used connector and theninserting and fixing the liner polarizer 18. In addition, a complicatedalignment step is also unnecessary, since only the linear polarizer 18is inserted into the slit 16.

The effectiveness of the polarizer-attached optical fiber connector 2depends on the selection of the linear polarizer 18. As previouslydescribed, the linear polarizer 18 has to be very thin in order tominimize the coupling loss. The linear polarizer must also have a highextinction ratio and a large aperture. Furthermore, it is preferablethat the linear polarizer be highly resistant to laser irradiation. Itis suitable that the linear polarizer 18 be a dichroic glass polarizerbeing marketed under the trademark “UltraThin™” by Corning. The“UltraThin™”-polarizer absorbs unpolarized components because it is adichroic glass polarizer.

“UltraThin™” has a thickness of about 30 μm, and the extinction ratio is40 dB and the insertion loss is 0.5 dB or less. That is, it is very thinbut is a high-function polarizer with a high extinction ratio and a lowinsertion loss. The “UltraThin™”-polarizer also has a largelight-receiving angle (±20°) and a large aperture diameter and has highresistance to laser irradiation. The “UltraThin™”-polarizer further hasa refractive index close to the refractive index of the core of theordinary optical fiber 10. The advantage of having a largelight-receiving angle is that the inclined angle of the slit 16 (where5° is preferred) with respect to the axial direction of the opticalfiber 10 can be effectively selected so that reflection at boundaries20, 22 is suppressed. The advantage of having a large aperture diameteris that the assembly step becomes simple. The advantage of having highresistance to laser irradiation is that the polarizer can be used evenwhen a high-power laser beam is employed. Since the refractive index of“UltraThin™” is nearly the same as that of the optical fiber core, theinsertion loss due to insertion of “UltraThin™” can be reduced and theshift of the optical axis of the fiber due to the inclination of thelinear polarizer is so small that it is negligible.

The polarizer-attached optical connector 2 is not limited to asingle-fiber connector. FIG. 3 shows a polarizer-attached opticalmulti-fiber connector 26. The polarizer-attached optical multi-fiberconnector 26 is equipped with a flat base plate 28. A slit array 31 isformed in the flat base plate 28. A polarizer insertion slit 30 isformed so that it crosses the slit array 31. The bare fiber portions 32of optical fibers 34 are disposed within the slit array 31. A linearpolarizer 38 is disposed within the insertion slit 30. The linearpolarizer 38 is inserted at an angle inclined slightly from a planevertical to the bare fiber portions 32. The linear polarizer 38 can be adichroic glass polarizer being marketed under the trademark “UltraThin™”by Corning.

In some applications, in the polarizer-attached optical fiber connector26 it is necessary to enhance the extinction ratio and then maintain thepolarization state. In such cases, the linear polarizer is installed inthe above-mentioned manner by employing a polarization maintaining fiberconnector in common use.

As described above, since no suitable linear polarizer had been put intopractical use, it has not been considered possible to install apolarizer in a connector, which is a relatively small optical component.The polarizer-attached optical fiber connector 2 according to thepresent invention is capable of producing a laser beam which has a highextinction ratio, by being applied to light sources and lighttransmission paths in currently use.

FIG. 4 shows a cross section of a polarizer-attached optical fiberconnector adapter 54, equipped with an adapter ferrule 53. Between twoadapter ferrules 53 a, 53 b, optical fibers 55 a, 55 b are installed.These adapter ferrules 53 a, 53 b are fixed to both surfaces of a linearpolarizer 52. They can be fixed, for example, with an adhesive. Thecontact surfaces between the adapter ferrules 53 a, 53 b and the linearpolarizer 52 are inclined with respect to the optical axes of theoptical fibers 55 a, 55 b. In other words, the linear polarizer 52 isdisposed in an inclined position with respect to the optical axes of theoptical fibers 55 a, 55 b. The linear polarizer 52 may be provided witha rotation mechanism (not shown) to obtain a desired polarizationdirection as required, by rotating the plane of the linear polarizer 52vertical to the optical axes of the optical fibers 55 a, 55 b.

FIG. 5 shows a cross section of a polarizer-attached optical fiberconnector adapter 64, equipped with an adapter ferrule 63. A slit 61 isformed within the ferrule 63 so that it reaches optical fiber bareportions 65 a, 65 b. Therefore, the optical fiber fixed to the adapterferrule 63 is divided into the two optical fiber bare portions 65 a, 65b by the slit 61. A linear polarizer 62 is inserted and fixed to theslit 61. The linear polarizer 62 can be fixed, for example, with anadhesive. The contact surfaces between the slit 61 and the linearpolarizer 62 are inclined from a plane vertical to the optical axes ofthe optical fiber portions 65 a, 65 b. That is, the linear polarizer 62is disposed in an inclined position with respect to the optical axes ofthe optical fiber portions 65 a, 65 b. The linear polarizer 62 may beprovided with a rotation mechanism (not shown) to obtain a desiredpolarization direction as required, by rotating the plane of the linearpolarizer 62 vertical to the optical axes of the optical fiber portions65 a, 65 b.

The polarizer-attached optical fiber connector adapter 64 is employed ina laser module (not shown), and the rotation axis of the polarizer 62can be aligned with the polarization axis of laser light produced by alaser diode. With this alignment, if only the polarizer-attached opticalfiber connector adapter 64 is connected to a laser module whoseextinction ratio is low, it becomes possible to produce laser lightwhich has a high extinction ratio. In addition, since the polarizer 62is the dichroic type, as described above, all of the unpolarizedcomponents are absorbed. Furthermore, the polarizer 62 is fixed at anangle inclined slightly from a plane vertical to the optical axes of theoptical fiber portions 65 a, 65 b so that the return light reflected bythe polarizer 62 is negligible. Therefore, the laser oscillation can bestably held. That is, it becomes possible to enhance the characteristicsof ordinary laser modules.

The polarizer-attached optical fiber connector adapter 64 can also beemployed as a common connector that is used in an optical transmissionpath. In this case, the extinction ratio of light propagating through anoptical transmission path can be enhanced. In other words, thepolarizer-attached optical fiber adapter fulfills the same function asthe fiber polarizer.

The above-mentioned polarizer-attached optical fiber connector adapter64 requires no addition of optical components and no special design,because it is manufactured by inserting and fixing the linear polarizer62 into the adapter ferrule 63 employed in a commonly used adapter.

The effectiveness of the polarizer-attached optical fiber connectoradapter 64 depends on the selection of the linear polarizer 62. Aspreviously described, the linear polarizer 62 has to be very thin inorder to minimize the coupling loss between it and the fiber. The linearpolarizer 62 must also have a high extinction ratio and a largeaperture. Furthermore, it is preferable that the linear polarizer 62have a high resistance to laser irradiation. It is suitable that thelinear polarizer 62 be the above-mentioned “UltraThin™” which is adichroic glass polarizer.

“UltraThin™” has a thickness of about 30 μm, the extinction ratiothereof is 40 dB and the insertion loss thereof is 0.5 dB or less. Thatis, it is very thin but is a high-function polarizer with a highextinction ratio and a low insertion loss. “UltraThin™” also has a largelight-receiving angle (±20° ) and a large aperture diameter and has highresistance to laser irradiation. “UltraThin™” further has a refractiveindex close to the refractive index of the core of the common opticalfiber 65 a or 65 b. The advantage of having a large acceptance angle isthat the inclined angle of the linear polarizer 62 (where 5° ispreferred) with respect to the axial direction of the optical fibers 65a, 65 b can be effectively selected so that the return light, which arereflected at the optical fibers 65 a, 65 b and the liner polarizer 62,is suppressed. The advantage of having a large aperture diameter is thatthe assembly step becomes simple. The advantage of having high laserresistance is that the polarizer can be used even when a high-powerlaser beam is employed. Since the refractive index of “UltraThin™” isnearly the same as that of the core of the optical fiber, the insertionloss due to insertion of “UltraThin™” can be reduced. Furthermore, theshift of the optical axis of the fiber due to the inclination of thelinear polarizer 62 is so small that it is negligible.

As described above, since no suitable linear polarizer had been put intopractical use, it has not been considered possible to install a linearpolarizer in an adapter which is a relatively small optical component.The polarizer-attached optical fiber connector adapter 64 according tothe present invention is capable of providing a laser beam which has ahigh extinction ratio, by being applied to currently used light sourcesand optical signal paths without addition of a lens, etc.

1. A polarizer-attached optical fiber ferrule comprising: an opticalfiber; a ferrule, fitted on the periphery of said optical fiber, andequipped with a slit reaching said optical fiber; and a linear polarizerhaving a thickness no greater than 50 μm inserted into said slit so thatit crosses said optical fiber.
 2. The polarizer-attached optical fiberferrule as set forth in claim 1, wherein said linear polarizer is adichroic glass polarizer.
 3. The polarizer-attached optical fiberferrule as set forth in claim 1, wherein said slit is inclined withrespect to an axial direction of said optical fiber.
 4. Thepolarizer-attached optical fiber ferrule as set forth in claim 1,wherein said fiber is a single mode fiber.
 5. The polarizer-attachedoptical fiber ferrule as set forth in claim 1, wherein said fiber is apolarization maintaining fiber.
 6. The polarizer-attached optical fiberferrule as set forth in claim 1, wherein said linear polarizer that isinserted has a polarizing angle which aligns with a polarizationdirection of a laser beam.
 7. The polarizer-attached optical fiberferrule as set forth in claim 1, wherein said optical fiber comprisestwo or more optical fibers.
 8. A polarizer-attached optical fiberconnector comprising: an optical fiber; a connector ferrule, fitted onthe periphery of said optical fiber, and equipped with a slit reachingsaid optical fiber; and a linear polarizer having a thickness no greaterthan 50 μm inserted into said slit so that it crosses said opticalfiber.
 9. The polarizer-attached optical fiber connector as set forth inclaim 8, wherein said linear polarizer is a dichroic glass polarizer.10. The polarizer-attached optical fiber connector as set forth in claim8, wherein said slit is inclined with respect to an axial direction ofsaid optical fiber.
 11. The polarizer-attached optical fiber connectoras set forth in claim 8, wherein said fiber is a single mode fiber. 12.The polarizer-attached optical fiber connector as set forth in claim 8,wherein said fiber is a polarization maintaining fiber.
 13. Thepolarizer-attached optical fiber connector as set forth in claim 8,wherein said linear polarizer that is inserted has a polarizing anglewhich aligns with a polarization direction of a laser beam.
 14. Thepolarizer-attached optical fiber connector as set forth in claim 8,wherein said optical fiber comprises two or more optical fibers.
 15. Apolarizer-attached optical fiber connector adapter comprising: anoptical fiber; two adapter ferrules fitted on the periphery of saidoptical fiber and fixed within an alignment sleeve; and a linearpolarizer inserted between said ferrules; wherein said fiber is apolarization maintaining fiber.
 16. A polarizer-attached optical fiberconnector adapter comprising: an optical fiber; an adapter ferrule,fitted on the periphery of said optical fiber, and equipped with a slitreaching said optical fiber; and a linear polarizer having a thicknessno greater than 50 μm inserted into said slit so that it crosses saidoptical fiber.
 17. The polarizer-attached optical fiber connectoradapter as set forth in claim 16, wherein said linear polarizer is adichroic glass polarizer.
 18. The polarizer-attached optical fiberconnector adapter as set forth in claim 16, wherein said slit isinclined with respect to an axial direction of said optical fiber. 19.The polarizer-attached optical fiber connector adapter as set forth inclaim 16, wherein said fiber is a single-mode fiber.
 20. Thepolarizer-attached optical fiber connector adapter as set forth in claim16, wherein said fiber is a polarization maintaining fiber.
 21. Thepolarizer-attached optical fiber connector adapter as set forth in claim16, wherein said optical fiber comprises two or more optical fibers.